Organic Reaction Mechanisms 1993

619 Pages·1995·18.951 MB·English

ORGANIC REACTION MECHANISMS 1993
*
ORGANIC REACTION
MECHANISMS 1993
An annual survey covering the literature
dated December 1992 to November 1993
Edited by
A. C. Knipe and W. E. Watts
University of Ulster
Northern Ireland
An Inferscience@ Publication
JOHN WILEY & SONS
- -
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Contributors
W. R BOWMAN Department of Chemistry, The University of Technology,
Loughborough, Leics, UK
M. R. CRAMPTON Department of Chemistry, Durham University, Durham, DHl
3LE, UK
R. G. COOMBES Department of Chemistry, Brunel, The University of West
London, Uxbridge, Middlesex, UB8 3PH, UK
N. DENNIS 3 Camphor-Laurel Court, Stretton, Brisbane, Queensland
41 16, Australia
G. W. J. FLEET Dyson Perrins Laboratory, Oxford University, South Parks
Road, Oxford OX1 3QT, UK
S. W. GINN School of Applied Biological and Chemical Sciences,
University of Ulster, Coleraine, Co. Londonderry, BT52
lSA, UK.
J. G. KNIGHT Department of Chemistry, The University, Newcastle-upon-
Tyne, NE1 7RU, UK
A. C. KNIPE Department of Applied Physical Sciences, University of
Ulster, Coleraine, Co Londonderry, BT52 lSA, UK
P. KOCOVSKY Department of Chemistry, The University of Leicester,
Leicester, LE1 7RH, UK
H. MASKILL Department of Chemistry, The University, Newcastle-upon-
Tpe, NE1 7RU, UK
A. W. MURRAY Department of Chemistry, The University, Dundee, DD1 4HN,
UK
M. I. PAGE Department of Chemical Sciences, The Polytechnic, Queens-
gate, Huddersfield, W Yorkshire, UK
J. SHORTER Department of Chemistry, The University, Hull, HU6 7RX,
UK
W. J. SPILLANE Department of Chemistry, University College, Galway, Ireland
J. H. STEWART School of Applied Physical Science, University of Ulster at
Jordanstown, Newton Abbey, Antrim BT37 OQB, UK
V
Preface
The present volume, the twenty-ninth in the series, surveys research on organic reaction
mechanisms described in the literature dated December 1992 to November 1993. In
order to limit the size of the volume, we must necessarily exclude or restrict overlap
with other publications which review specialist areas (e.g. photochemical reactions,
biosynthesis, electrochemistry, organometallic chemistry, surface chemistry and
heterogeneous catalysis). In order to minimize duplication, while ensuring a
comprehensive coverage, the editors conduct a survey of all relevant literature and
allocate publications to appropriate chapters. While a particular reference may be
allocated to more than one chapter, we do assume that readers will be aware of the
alternative chapters to which a borderline topic of interest may have been preferentially
assigned.
There have been two changes of authorship since last year. We say farewell to Prof. R.
A. Aitken (Carbenes and Nitrenes) and Dr A. Thibblin (Elimination Reactions) and
wish to express our thanks for the expert contributions which they have made to the
series over a prolonged period. Their respective chapters have been entrusted to Dr J. G.
Knight (University of Newcastle) and Prof A. C. Knipe (University of Ulster).
Once again we wish to thank the publication and production staff of John Wiley &
Sons and our team of experienced contributors for their efforts to ensure that the
standards of this series are sustained. We are also indebted to Dr N. Cully, who
compiled the subject index.
A.C.K.
W.E.W.
vii
CONTENTS
1. Reactions of Aldehydes and Ketones by M . I . Page .......... 1
2 . Reactions of Acids and their Derivatives by W. J. Spillane ..... 17
3 . Radical Reactions: Part 1 by W. R . Bowman .............. 67
.
4 Radical Reactions: Part 2 by S . W. Ginn J. H . Stewart ..... 103
and
5 . Oxidation and Reduction by G . W. J . Fleet ................ 151
6 . Carbenes and Nitrenes by J. G . Knight .................. 183
.
7 Nucleophilic Aromatic Substitution by M . R . Crampton ....... 201
.
8 Electrophilic Aromatic Substitution by R . G . Coombes ....... 221
9 . Carbocations by H . Maskill .......................... 235
.
10 Nucleophilic Aliphatic Substitution by J. Shorter. ........... 263
.
11 Carbanions and Electrophilic Aliphatic Substitution
by A . C . Knipe ................................... 297
12. Elimination Reactions by A . C . Knipe ................... 333
.
13 Addition Reactions: Polar Addition by KoEovslj ......... 355
. P.
14 Addition Reactions: Cycloaddition by N . Dennis ........... 395
.
15 Molecular Rearrangements by A . W. Murray ............. 437
AuthorIndex ........................................ 561
Subject Index ........................................ 605
CHAPTER 1
Reactions of Aldehydes and Ketones and their Derivatives
M. I. PAGE
Department of Chemical and Biological Sciences, University of Huddersfield
Formation and Reactions of Acetals, Ketals, and Orthoesters ............ 1
Hydrolysis and Formation of Glucosides, Nucleosides, Oxazines,
and Related Compounds .................................. 3
Reactions and Formation of Nitrogen Derivatives, Schiff Bases,
Hydrazones, Oximes, and Related Species ....................... 4
C-C Bond Formation and Fission: Aldol and Related Reactions . . . . . . . . . . 6
Other Addition Reactions ................................... 8
Enolization and Related Reactions ............................. 10
Hydrolysis and Reactions of Vinyl Ethers and Related Compounds . . . . . . . . 11
Other Reactions ......................................... 12
References. ............................................ 13
Formation and Reactions of Acetals, Ketals, and Orthoesters
There has long been unequivocal evidence that ring opening during the acid-catalysed
hydrolysis of cyclic acetals can be reversible.' Generation of the o-hydroxyalkyloxy
carbocations (1) from vinyl ethers of acetophenone shows that trapping the intermediate
by water is an order of magnitude faster than intramolecular ring closure. The slower
rate of hydrolysis of the corresponding cyclic acetals, compared with their acyclic
analogues, cannot be due to reversible ring opening.2
The mechanism of the acid-catalysed hydrolysis of 2-substituted 1,3-dithianes
changes from ASE2 for the most reactive thioacetals to A2 for the least reactive. In
concentrated acid, the carbocations (2) are generated which react irreversibly with water
to give the corresponding benzophenone via the hemithi~acetal.~
The a-deuterium secondary kinetic isotope effect for the uncatalysed hydrolysis of 2-
(3) is 1.17, at consistent with rate-limiting
(4'-nitrophenoxy)tetrahydropyran 46"C,
i~nization.~
The acid-catalysed ethanolysis of substituted di- 1- azulenyl ketones (4) gives
substituted azulenes and ethyl azulene- 1- carboxylates derived from CCO cleavage.
Protonation of the carbonyl oxygen generates a tropylium-like cation and cleavage of
the hemiacetal intermediate (5) generates the product^.^
Base-catalysed aced formation from carbohydrate epoxides is thought to occur by
intramolecular ring closure of the hemiacetal anion, opening the epoxide (6).6
Organic Reaction Mechanisms I993 Edited by A. C. Knipe and W. E. Watts
01995 John Wiley & Sons Ltd
1
Organic Reaction Mechanisms 1993
There is an inverse relationship between the rates of heterocyclic acetal hydrolysis
and their inhibitory effect on the enzyme monoamine oxidase, which is taken to
indicate that the enzyme adduct is electronically stabilized by the heterocycles.’
DDQ in wet ethyl acetate catalyses the
(2,3-dichloro-5,6-dicyano-p-benzoquinone)
hydrolysis of acyclic acetals by acting as a Lewis acid.8
1,3-Dioxolanes are oxidized by iodine monochloride to the appropriate oxocarbocat-
ions (7), which either react with chloride ion to give chlorohydm esters with inversion
of configuration or diol monoesters with retention of configuration. The more stable
carbocations are susceptible to attack by water on the central carbon.’
A neighbouring hydroxyl group can control the stereoselectivity of spiro ketal
formation by magnesium ion chelation.’O The stereoselective reduction of spiro ketals
can be achieved by DIBAH and a silane Lewis acid which is attributed to steric
hindrance of a-methyl groups at the spiro ketal centre and to vicinal ether oxygens used
for bidentate chelation.”
Cyclization of a chiral hydroxy ketone to a hemiacetal occurs stereoselectively, which
can be rationalized by steric effects.’*
The stereoselective synthesis of dioxolane-type endo-benzylidene acetals can be
’
performed stereoselectively under kinetically controlled conditions.
Bicyclic ketals (8) are precursors of the corresponding diketones and dioximes from
which 2,6-disubstituted pyridines can be synthesized. Isotopic labelling identified the
presence of the di~xime.‘~
The stereoselective formation of cyclic acetals from pentane-l,3,5-triols relies on
attractive van der Waals interactions.15
The acid-catalysed cyclotrimerization of aliphatic aldehydes to give 2,4-6-trialkyl-
1,3,5-trioxanes by heteropoly acids can occur with a phase separation due to the
insolubility of the coordinated acid and aldehyde.16
Possible mechanistic pathways have been proposed to explain unexpected products in
the acid-catalysed reactions of terpenic ketones and aldehydes with alcohol^.'^ A
thiazolium salt is an efficient catalyst for the formation of ketals in alcoholic carbonate
solutions.’8 Chiral acetals can be synthesized from the Pd(I1)-catalysed addition of
methanol to alkenes.”
1 Reactions of Aldehydes and Ketones and their Derivatives 3
A reversal of the usual reactivity of primary and secondary alcohols towards
electrophiles can be achieved by the conversion of 1,2-diols into hexamethylene-
stannylene acetak20
Hydrolysis and Formation of Glucosides, Nucleosides, Oxazines,
and Related Compounds
Stereoelectronic effects in glycoside hydrolysis have been reviewed and the principle of
least motion hypothesis criticized. With little supporting evidence, but many assertions,
detailed reaction pathways are outlined including one for the acid-catalysed hydrolysis
of cr and p-methoxytetrahydropyrans to explain the 1.5-fold rate difference!21
It is often assumed that carbohydrates cyclize kinetically to five-membered ring
acetals but slowly rearrange to the thermodynamically more stable six-membered rings.
The acid-catalysed cyclization of ketones can give either
3-substituted-4,5-dihydroxy
tetrahydropyran or tetrahydrofuran acetals; syn 3,4-substitution (9) gives the six-
membered ring whereas the anti isomer gives exclusively the five-membered ring.22
The equilibrium concentration of the open-chain keto form Of D-fiuCtOSe is 0.8%a nd
almost invariant with pH, as determined by FTIR studies.23
As expected, a p-trimethylammonium substituent decreases the pH-independent
hydrolysis of 1- phenyl$-D-ribofoside compared with a p-nitro ~ubstituent.~~
The rate of the acid-catalysed ring opening of b-cyclodextrin is inhibited by guest
molecules. The deceleration in rate is directly related to the strength of a~sociation.~~
Eight-membered benzylidene acetals bridging the two monosaccharide components
of cr-maltosides are readily formed using cr, a-dimethoxytoluene, but may be selectively
hydrolysed by 80% acetic acid at room temperature.
4 Organic Reaction Mechanisms 1993
The reaction of 2-amino-2-deoxy sugars with isocyanates gives initially ureido
derivatives which, under acidic conditions, give the trans isomers (10) which
consequently ring close to the cis-fused glucofuranoses (1l ).27
The formation of 2-deoxyglycosides proceeds through the intermediate formation of
a charge-transfer complex of dimethoxyphenylmethyl glycosides with 2,3-dichloro-5,6-
dicyano-p-benzoquinone (DDQ) in the presence of alcohols acting as glycosyl
acceptors.28
The different reactivities of ribonolactones with benzaldehyde and acetone in acidic
media are associated with relatively minor changes in structure which are difficult to
predict.29
The stereo-controlled glycosidation of secondary sugar hydroxyls to give
disaccharides containing 1,2-cis-glycoside linkages, using silicon as a tethering step,
involves an intramolecular di~placement.~~
Reactions and Formation of Nitrogen Derivatives, Schiff Bases,
Hydrazones, Oximes, and Related Species
The 0-acetyl group in (12) is orthogonal to the benzene ring, in the crystal state, which
is attributed to dipole repulsion between the imine and the carbonyl group.
Tautomerism and isomerization in this system are also disc~ssed.~’
The E-2 thermal isomerization of N-benzylideneanilines (13) can occur through
perpendicular or planar conformations. The mechanism adopted is a sensitive function
of substituents.
The site of protonation, C or N, in cyclic a-ketoenamines varies with ring size. For
example, the cyclohexene derivative is protonated on the heteroatom (14), whereas the
seven-membered derivative is also protonated at C(3).33
0 n
H
\ 111. Me
IC= N\
Ar Ar
H ~ H O H
\ /
SAr
ArCo\ /
N=C
,CH \
HN C1
(16)
There have been further reports on the formation and hydrolysis of Schiff bases of
pyridoxal 5’-phosphate with hexylamine. The dehydration of the intermediate
carbinolamine is assumed to be rate-limiting catalysed intramolecularly by the
and
phenolic group. The rates of reaction can be correlated with the difference in the pK, of
the ammonium ion the pyridoxal phosphate.34
and